1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and more particularly, to a semiconductor integrated circuit reducing the stray capacitance in the output side of a capacitive coupled circuit.
2. Description of the Prior Art
Description is now made of a conventional semiconductor integrated circuit for propagating signals through a capacitive element. FIG. 1 is an equivalent circuit diagram of such a conventional circuit and FIG. 2 is a layout diagram showing a typical example of the layout of such a circuit. In these drawings, a capacitive element 3 is formed by a first conductor 1 and a second conductor 2. The first conductor 1 is connected to an input terminal 5 and the second conductor 2 is connected to an output terminal 6, respectively. Numeral 4 indicates the stray capacitance generated in the second conductor 2.
Assuming that the input signal voltage applied to the input terminal 5 is represented by V.sub.1 and the capacitance of the capacitive element 3 is represented by C.sub.C while the stray capacitance 4 is represented by C.sub.S and the output signal voltage propagated to the output terminal 6 is represented by V.sub.2 in the above circuit, the relation between the input voltage V.sub.1 and the output voltage V.sub.2 is expressed as follows: ##EQU1##
In the conventional circuit, the input voltage V.sub.1 and the output voltage V.sub.2 are in the relation as expressed by the above equation (a), and hence it is necessary to increase the capacitance C.sub.C or decrease the stray capacitance C.sub.S to extract a high output voltage. However, the area of the second conductor 2 must be enlarged for increasing the capacitance C.sub.C whereby the stray capacitance C.sub.S is inevitably increased, leading to contradiction in the above relation and difficulty in correct propagation of fine signals.
Improvements in capacities of capacitive elements are disclosed in Electronic Engineer June, 1980, pp. 91-92 and U.S. Pat. No. 4,075,509 issued on Feb. 21, 1978.